The comment about doing it open loop is, in my opinion, utter rubbish. There is absolutely no reason why a closed loop system will give you more problems. What it will do is give you better economy and allow you to check that the engine never runs lean even at maximum load. As we all know, running a standard engine lean for any length of time really can lead to problems.We nearly always close loop older vehicles and results are, without doubt, better than open loop.

A correctly setup open loop system will give just as good fuel consumption as a closed loop mixer. You can improve the closed loop by adding a TPS switch. A closed loop system does not in anyway insure that you do not get lean running but it can help.

The advantage of open loop is the only things that can go wrong are 1) switch - can be bypassed with a piece of wire2) solenoids - can be bypassed with a spanner to get you out of trouble3) vapouriser - you are driving home on petrol if it has gotten very bad

Closed loop has the above +

4) ECU failure5) stepper motor - can be bypassed with a open loop adjuster6) lambda sensor failure, depending how it fails you might not be aware other than poor consumption

Older engines if burning oil are going to get a lot of Lambda issues as they will soot up giving false lean readings. The is no harm is fitting a lambda boss for setting up and later checking with the hole blanked off when not in use.

If I was going to all that hassle I would go the next step with stand alone engine manangemnt with programmable ignition and fuel injection.

Thanks chaps. I can see the pros and cons. I'm very familiar with old carburettors so in that sense an open loop system is kind of what I know best. On the other hand I've done lots of vehicle projects involving wiring modifications and parts fabrication and I'm good with electro-mechanical stuff and processors (one of my other interests is restoring solid state pinball machines) so rigging up TPS etc. and getting it all working together shouldn't be too unfamiliar either.

I'm not too bothered about (detectable) system faults as either way the final resort is petrol.

To answer Simon's post:

The camper is build by Winnebago around a Dodge van chassis and cab. It's not a full size Winnebago; they officially called it the "Mini Winnie".

The engine is actually somewhat newer than the rest of it, but still carbureted with a conventional distributor etc. It appears to be in good nick but I'll be doing a compression check. It was manufactured to run on unleaded (the yanks went to unleaded around 1973). I may look at a cam change and I will definitely be upgrading the ignition system as both valve and ignition timing on these engines tend to suffer from having to meet American emissions Regs (which also started in the early '70s). Other than that it will be staying standard unless I decide to swap on some higher compression heads that I happen to have left over from another project, that is if I find an inlet manifold to suit them.

The air filter is the typical after-market circular sandwich type with the filter paper exposed around the outside but I'm not stuck with that. I think there's a fair bit of space around and above it but I can't check right now as I haven't picked it up yet !

It's going to be mostly just plodding along so I guess I don't need to worry too much about high revving "performance" capabilities. I'm also guessing that it works out cheaper to pick up an entire compatible LPG system rather than trying to piece one together myself.

I'm not in any big rush and there are other unrelated jobs I want to do on it so I can take my time finding something. I've seen Impco mentioned for American stuff, not sure what else would work but presumably some of the larger Rover/Jeep type systems assuming they're not multi-point.

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